Electrophysiological evidence for automatic processing of erroneous stimuli.

In a paradigm combining color-word Stroop and misspelled words processing, spelling mistakes were placed in half the Stroop stimuli. Participants were presented with words written in different ink colors and asked to identify the color of the ink while ignoring the word meaning. Importantly, whether the word was correctly spelled or not was completely irrelevant to the task. The spelling manipulation did not change the phonology or semantic meaning of the words. Congruency and spelling correctness were manipulated orthogonally and interacted at the behavioral level. Event-related potentials showed a very early processing of misspelled words. The present findings are in line with the idea of anterior cingulate cortex (ACC) involvement in cognitive monitoring, expressed mainly in the theta frequency band. The present study demonstrates that this monitoring mechanism is elicited automatically, in other words, this mechanism perceives erroneous stimuli even when they are absolutely irrelevant to the participant׳s task. At later processing stages, the same central monitoring mechanism is also involved in the detection/resolution of conflict.

Theta synchrony supports Weber-Fechner and Stevens' Laws for error processing, uniting high and low mental processes.

Human brain theta rhythm has been related to the operation of a generic mechanism involved in error detection processes of different types (e.g., detecting incorrect motor responses or incorrect arithmetic equations). This theta activity seems to be sensitive to error salience or magnitude, that is, stronger theta activity is found with larger or more deviant errors (e.g., 1+2=8) than with smaller or less deviant ones (e.g., 1+2=4). A time-frequency decomposition analysis indicated that theta activity is modulated by the magnitude of erroneous information in a nonlinear fashion, which can be characterized using Weber-Fechner's law of logarithmic function and Stevens' law of power function. The present study suggests that the generic mechanisms for error detection and evaluation may share similar fundamental neural schemes with primary cognitive and sensory or perceptual processes, which are directly involved in processing the specific type of input.

Fast and slow brain rhythms in rule/expectation violation tasks: focusing on evaluation processes by excluding motor action.

Theta rhythm has been connected to ERP components such as the error-related negativity (ERN) and the feedback-related negativity (FRN). The nature of this theta activity is still unclear, that is, whether it is related to error detection, conflict between responses or reinforcement learning processes. We examined slow (e.g., theta) and fast (e.g., gamma) brain rhythms related to rule violation. A time-frequency decomposition analysis on a wide range of frequencies band (0-95 Hz) indicated that the theta activity relates to evaluation processes, regardless of motor/action processes. Similarities between the theta activities found in rule-violation tasks and in tasks eliciting ERN/FRN suggest that this theta activity reflects the operation of general evaluation mechanisms. Moreover, significant effects were found also in fast brain rhythms. These effects might be related to the synchronization between different types of cognitive processes involving the fulfillment of a task (e.g., working memory, visual perception, mathematical calculation, etc.).

When things look wrong: theta activity in rule violation.

A violation of a rule or expectation is known to evoke a phasic negative potential over the medial frontal cortex. This electrophysiological effect has been shown for incorrect mathematical equations and incongruent words at the end of sentences. The cognitive processes elicited in rule violation seem to involve violation of expectation, error detection, and conflict between competing cognitions. Consistent with the conceptual relation between rule violation and error/conflict detection, rule violation conditions should involve a power increase in the theta frequency band involving the anterior cingulate cortex (ACC). The present study verifies the connection between rule violation and theta activity using a wavelet analysis. Moreover, low resolution brain electromagnetic tomography (LORETA) source localization connects this theta activity to the ACC. Furthermore, the results show that theta activity is sensitive to the salience of the violation, that is, the degree of deviation of the conflicting/erroneous stimulus from the correct (expected) one.

Infant brains detect arithmetic errors.

A current debate is whether increased looking time in infancy is related to violation of expectations. In this study, 6- to 9-month-old infants' brain activity was analyzed during presentation of correct and incorrect solutions to simple arithmetic equations [(e.g., presentation of 1 + 1; one doll on a TV monitor, with another doll added from behind a screen, followed by a solution of 2 (correct) or 1 (incorrect)]. Infants looked longer at incorrect solutions than at correct ones. Event-related potentials, time-locked to the presentation of the solution, also differed between conditions, with greater negative activity for the incorrect solution condition. Spectral analysis showed a similar pattern to that of adults observing correct and incorrect arithmetical equations. These findings show (i) that the brain network involved in error detection can be identified in infancy and (ii) that this network can support an association between looking time and violation of expectations.

Motor and non-motor sequence learning in children and adolescents with cerebellar damage.

Cerebellar involvement in motor and non-motor sequence learning was examined with serial reaction time tasks (SRT). Our sample consisted of 8 children and adolescents who had undergone surgical removal of a benign posterior fossa tumor (PFT) during childhood. None of them had undergone chemotherapy or cranial radiation therapy (CRT). Ages ranged from 1-11 years at surgery and 9-17 years at testing. The children were tested not earlier than 2.5 years after surgery (M = 5.9 years), enabling brain plasticity and recovery of functions. Their performance was compared with a matched control sample. The PFT group was not impaired in the implicit learning of sequences, as reflected in their performance in blocks with a repeated sequence, both before and after a random block. However, in the perceptual task, their performance deteriorated more than that of the control group when a random block was introduced, suggesting that it was more difficult for the patients to respond flexibly or change their response set when encountering changing task demands. These results are in line with another study by our group on task switching with the same patients.

Task switching after cerebellar damage.

The authors of this study investigated task switching following cerebellar damage. The study group consisted of 7 children and adolescents (M age=13.8 years) who underwent surgical removal of a benign posterior fossa tumor. They were tested at a sufficient interval after surgery (M lag=6.13 years) for restoration of normal cognitive skills and intelligence. Although all showed normal learning of the task compared with control participants, when rapid behavioral changes were required (short preparation time), they exhibited behavioral rigidity manifested by enhanced switching cost. These results are in line with another study on serial reaction time with the same patients (A. Berger et al., in press). They have important implications for our understanding of the cognitive sequelae of early cerebellar damage as well as the involvement of the cerebellum in task switching.